This invention is directed to an improved nonaqueous slurry suitable for use as a thickener or viscosifier in oil or gas drilling, fracturing, flow diversion, completion or workover fluids, which slurry comprises a water-soluble cellulose ether polymer, a water-insoluble liquid hydrocarbon, a non-ionic surfactant having an HLB of from about 7 to about 14, and an organo modified clay. The slurry may include a thermal stabilizer. Additionally, this invention is directed to a process for thickening oil or gas drilling, fracturing, flow diversion, completion or workover fluids which comprises adding thereto the non-aqueous slurry as heretofore described.
Many polymeric containing formulations suitable for use as thickeners in oil or gas drilling, fracturing, flow diversion, completion or workover fluids are not storage stable over long periods of time. Therefore, the ingredients are supplied in a dry state. When the polymer, for example, hydroxyethyl cellulose, is added to an oil field brine, many complications due to lumps of unhydrated polymer, commonly known as "fish-eyes" can occur. Fish-eyes can cause well damage by plugging performations or plating out on the formation during open hole operations. Lumps or fish-eyes also form during the addition of dry polymers to water because the polymer molecules are not adequately dispersed before they begin to hydrate. Once the outer layer of the polymer is hydrated, the fish-eyes cannot be dispersed. The only way to insure rapid and complete yielding of the polymer is to disperse the polymer particles before hydration begins.
Due to such problems, the trend in the industry has been toward a liquid dispersion containing a polymeric viscosifier in a dispersed unhydrated state. The liquid viscosifiers are highly desirable in drilling, workover, completion and fracturing fluid applications where inadequate polymer mixing equipment exists.
A produce announcement titled "K 8D30--A fine-mesh biopolymer for liquid viscosifiers" (published by Kelco, Division of Merck & Co., Inc., dated 4/79) describes a liquid viscosifier containing a high molecular weight biopolymer. This publication describes that if the polymer is dispersed in an oil prior to addition to the aqueous fluid, the problems with lumping, fish eyes, etc. are basically eliminated. Two formulations are described in the publication. A formulation which contains a low biopolymer concentration (30%) includes mineral oil, organophilic clay, surfactant (Tergitol 15-S-3) and biopolymer. A high biopolymer concentration (50%) formulation includes lauryl alcohol, methanol, hydroxypropyl cellulose, kerosene, lecithin, and biopolymer. This publication further states that the mineral oil can be substituted with vegetable oil or animal oils that have a viscosity of at least 100 centipoise. Also, the publication states that the organophilic clay is not required at biopolymer concentrations of less than 30%. Further, the publication states that the surfactant aids in dispersion of the slurry when added to water and that other ethoxylated linear alcohols can be substituted for the Tergitol surfactant.
U.K. Patent Application No. 2000799A describes compositions suitable for use in the preparation of cellulose ether-containing drilling fluids. These compositions are concentrated liquids used as rapidly dissolving thickeners. Said U.K. Application describes that when drilling for oil or natural gas, use may be made in a particular oil sand of a drilling fluid to which the composition has been added either previously during the preparation of the drilling fluid or in the well during the drilling process. The compositions are described as containing 2 to 65% of a water-soluble cellulose ether; 30-95% of a water miscible glycol ether and 0.5-40% of water, with the percentage of water being less than that of the water-miscible glycol ether. This U.K. Application states that the composition can also contain bentonite clay in an amount which is 2 to 30% of the sum of the amounts by weight of cellulose ether, glycol ether and water. Additionally, the U.K. Application states that the compositions can contain a petroleum product boiling within the range of 150.degree. to 400.degree. C. in an amount which is from 30 to 150% by weight of the total weight of cellulose ether, glycol ether and water. Examples 5 to 8 of the U.K. Application describe compositions containing fuel oil, clay, glycol ether, cellulose ether and small amounts of water. However, this patent does not disclose the use of a non-ionic surfactant in the compositions.
A commercially available liquid slurry (Liqui-Vis sold by NL Baroid Company) used as a thickener contains hydroxyethyl cellulose, a water-insoluble liquid hydrocarbon (diesel oil), clay, and an anti-foam agent.
U.S. patent application Ser. No. 136,762 filed Apr. 3, 1980, titled "Rapidly Dissolved Water-Soluble Polymer Composition", now U.S. Pat. No. 4,325,861 (Braun et al.), describes water-soluble polymers rapidly dissolved by employing a concentrate of (a) a water-soluble particulate polymer, (b) a water-insoluble organic vehicle which is a non-solvent for the polymer, (c) an inert, nonionic surfactant agent compatible with the organic vehicle in sufficient amounts to remove said organic vehicle coating on said particulate polymer upon dilution with water, and (d) an inert thickener agent in amounts of from about 0 to 5% by weight of the composition to retard stratification of the composition when fluidized. The nonaqueous slurries are described as useful as lubricants when dissolved in aqueous solutions.